1. Field of the Invention
This invention relates generally to fastener driving tools, and particularly to driving tools that utilize an energy storing flywheel that selectively engages a ram in order to drive the ram into engagement with a fastener such as a nail or a staple in order to drive the fastener into the workpiece.
2. Description of the Prior Art
Several fastener driving tools that utilize an energy storing flywheel for the purpose of storing energy to drive the fastener into the workpiece are known. Examples of representative prior art devices are disclosed in U.S. Pat. Nos. 4,042,036; 4,121,745; 4,129,240; 4,189,080; 4,298,072; 4,290,493 and 4,323,127. While the devices disclosed in the above references are capable of driving fasteners such as nails or staples into a workpiece, they do suffer from several disadvantages, including excessive weight and less than optimum balance. These disadvantages present a particular problem in devices that employ more than one flywheel, especially those devices that utilize a separate motor to drive each of the two flywheels. In addition, the prior art devices utilize a high friction material such as brake lining or similar material that is disposed on the surface of the ram or on the periphery of the flywheel. Unfortunately, such material is subject to wear because of the high relative speed between the surface of the flywheel and the surface of the ram that is present when engagement occurs. Also, the high pressure exerted on the brake material causes the material to crumble prematurely. As a result, the ram or the flywheel must be frequently replaced. Also, in the prior art devices, neither the ram nor the flywheel is readily accessible, and consequently the replacement of these components tends to be time consuming and costly. Finally, the prior art devices utilize a resilient member for returning the ram to a rest position, and in the prior art devices, the resilient member tends to fatigue and fail after a moderate number of fasteners have been driven.